連接數據庫步驟：

註冊驅動：Class.forName("com.mysql.jdbc.Driver");

設置數據庫地址、用戶名、密碼：String url = "jdbc:mysql://localhost:3306/database";

創建連接：Connection conn = DriverManager.getConnection(url, username, password);

創建sql語句字符串：String sql = "insert into tb_books(name,price,bookCount,author) values(?,?,?,?)";

使用PreparedStatement處理sql語句：PreparedStatement ps = conn.prepareStatement(sql);

設置缺省數據：ps.setString(1, variable);

執行sql語句，返回受影響行數：int row = ps.executeUpdate();

釋放對象：ps.close();

關閉連接：conn.close();

    out.println(request.getParameter("price"));
    double price = Double.parseDouble(request.getParameter("price"));
    out.println(price);
    try {
        Class.forName("com.mysql.jdbc.Driver
 
");
        String url = "jdbc:mysql://localhost:3306/test";
        String username = "root";
        String password = "123456";
        Connection conn = DriverManager.getConnection(url, username, password);
        String sql = "insert into tb_books(name,price,bookCount,author) values(?,?,?,?)";
        PreparedStatement ps 
 
= conn.prepareStatement(sql);
        ps.setString(1, book.getName());
        ps.setDouble(2, price);
        ps.setInt(3, book.getBookCount());
        ps.setString(4, book.getAuthor());
        int row = ps.executeUpdate();
        if (row > 0) {
            out.print("成功添加了" + row + "條數據！");
        }
        ps.close();
        conn.close();
    } catch (Exception e) {
        out.print("添加失敗！");
        e.printStackTrace();
    }

    try {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/test";
        String username = "root";
        String password = "123456";
        Connection conn = DriverManager.getConnection(url, username, password);
        if (conn != null) {
            out.println("success!!");
            conn.close();
        } else {
            out.println("fail");
        }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }

Q：輸入的是小數，但是存入之後顯示的是四舍五入後的整數。

A：float最多表示7位有效數據。double最多表示16位有效數據。改了double類型的位數為0，就好了。

JDBC及常見數據存取問題